Photoflash lamp



Nov. 5, 1957 c. M. RlvELY 2,811,846

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Z a0 ,7.a da ..0 n/ a 9 7 5ML W United States Patent PHoroFLAsH LAMP Clair M. lively, Rockaway, N. J., assignor to Westinghouse Electric CorporatiomEast Pittsburgh, Pa., a corporation of Pennsylvania Application May 29,1953, SerialNo. 358,415

4 Claims. (Cl. 67.'-31) This' invention relates to theY manufacture of photoflash lamps, and more particularly, to suchl of an4 improved and simplified construction.

The principal object of my invention, generally considered, is to produce a photoflash` lampv which is very economically manufactured andv has a plastic basecarrying a primer, together with means for manufacturing, and apparatus for` operating such lamps after manufacture.

Another object of my invention is to simplify the method of manufacturing photoiiash lamps so that the bulbs thereof may be exhausted. and gas-filled simultaneously with the application of plastic bases thereto.

A further object of my invention is t produce apparatus for manufacturing photoiiash lamps, whereby plastic bases for such are softened and applied to the necks of the bulbs therefor, while said: bulbs are being exhausted and filled with oxygen.

A still further object of my invention; is to produce a photoliash lampin whichtheneck of the bulbis embedded in a` block of plastic forming the base, one or more leads passing through said plastic base and carrying the primer, the latter being ignitable by either aspark or. an incandescible filament, depending on, the type of lamp.

An additional object of my invention is` to provide apparatus for effectively operating or igniting photoliash lamps of the type above identified.

Other objects and advantages of the invention will become apparent as the descriptionr proceeds.

In the drawing:

Fig. 1 is an elevational view of 'a'.photoashlamp'. em-y bodying my invention.

Fig. 2 is a base end view ofl the lamp of Fig: 1.'.

Fig. 3 is a fragmentary axial; sectional'view of the lamp of Fig. 1, on an enlarged scale.

Fig. 4 is a wiring diagram of apparatus for operating or igniting photoiiash lamps embodyingmy invention.

Fig. 5 is an elevational View, with parts in axial section, of a photoflash lamp embodyingmy. invention associated. with apparatus for operating or igniting thezsamef.

Fig. 6 is a view similar to Fig. 5, but showing av modification.

Fig. 7 is a fragmentary elevational view of apparatus which may be employed for'producing. the lead portions of mounts for lamps embodying my invention.

Fig. 8 is a view similar to` Fig. T, but showing a subsequent stage in the process of preparing such leads.

Fig. 9 is an end view on theline-IX-IX of Fig. 7, in the direction of the arrows, but `showing-the cutting jaws separated.

Fig. 10 is a fragmentary elevational view illustrating the first step in the manufacture of a mount for a. photoflash lamp embodying my invention, wherein a lead is being embedded into a base blank.

Fig. 11 is a View similar to Fig. 110, but showing a modification.

Fig. 12 is an elevational view, with parts in axial section, showing apparatus which maybe employed" for 2. applying a primer tova mount of a photoash lamp embodying my invention.

Fig. 13 is an elevational view, with parts in axial section, of apparatuswhich may beemployed for softening the base, exhausting, gas-filling, and embedding the lower edge of the bulb neck in` said softened base.

Fig. 14 is a fragmentary view of the apparatus of Fig. 13, but showing a subsequent position in which a base has been actually sealed to the neck of a bulb, after said bulb has been exhausted and oxygen-iilled.

Fig. 15 is a front elevational view similar to Fig. l, but showing a modified form of photoash lamp.

Fig. 1.6 is a sectional View on the line XVI-XVI of Fig. 15.

Fig. 17 isa side elevational view of a lamp like that of Fig. 15, looking from the right, but with a modified base..

Fig. 18 is a fragmentary vertical sectional view of part of. the apparatus` for molding plastic bases around leads to form mounts for lamps such as illustrated in Figs. 15, 16.and 17.

Fig. 19 is a view corresponding toFig. 1S, but showing a subsequent position in which an upper mold has been brought over the lower mold of Fig. 18, to finish molding the. plastic base and embedded leads forming a mount.

Fig. 20 is an elevational View corresponding to Fig. 15, but; showing another embodiment of my invention.

Fig. 21 is agraph showing, the light iiux vs; time characteristics of a photoiiash lamp as illustratedV in Figs. 1, 2 and 3.

Fig, 22 is a similar graph for a commercial No. 5

photolash lamp as manufactured by theassignee of thev while'the inner end thereof carries a primer or mass of' priming material 26.

ln the present embodiment, the lead 25 :carries insulating,l desirably plastic, material 27,.which projects a slightI distance beyond the inner end of the lead 25, soas to.

lea-ve a cavity or spark gap 28, whichimay be formed of a desired: length, between the inner end ofl said wire and the. priming material 26, for igniting purposes. The envelope as is customary, contains combustible material 29; such as shredded aluminum and/or magnesium in auatmosphere of oxygen or other combustion-supporting` gas;

The` primer is situated` on theA plastic coated end of the wire 25 for its better support. The cavity or spark gap 23 is` formed adjacent. the end of the plastic coating and enclosed by the primer, so that the igniting spark tires the primer onl the inside of the cavity. The delay produced by burning through the primer before it cany ignite the surrounding combustible4 material is desirable, ifl the spark fired lamp is tol haveY characteristics comparable with those of the standard #-'Slampas manufactured by the assignee ofv the present application.

Referring to` Figure 2l which. shows thefiring charac? teristicsv of a, lamp embodying theform of my invention illustrated. in Figs. l, 2 and 3, it will be seen. that with the. gap 0r cavity 2,8 adjusted, that, is, about .1.l in length.

to give the proper size spark and the thickness of, the primer 26 adjusted to provide the desired'delay in burning through said primer prior to ignition of the combustible material, thereabout we have, after a peak at 125 which represents the primer ash, the light flux reaching a maximum at about 20 milliseconds, which compares with a light fiux peaking at about 20 milliseconds in the commerical #5 photoilash lamp, as illustrated in Fig. 22.

The Vslight peak at milliseconds, shown in Fig. 22, represents the filament-ignited primer flash which, as will be seen, occurs later than the spark-ignited primer flash of the first embodiment of my invention, because of the time delay in incandescing the filament to ignite the outside of the priming material on the ends of the leads, such as those designated 2Sa and 73 in Fig. 15. However, because the filament affects outside ignition of the primer, combustion is thereafter more rapid than in the case of inside ignition of the primer of a lamp such as illustratedin Figs. 1, 2 and 3, so that the peak is reached in both cases at about milliseconds.

It will, therefore, be seen that lamps manufactured in accordance with the first embodiment of my invention may be controlled, not only by the amount of combustible material, pressure of the combustion-supporting atmosphere, and the size of the bulb, but additionally by the amount and distribution of the primer, which is ignited on the inside rather than the outside, and the length of the spark gap or cavity 28.

The lamp of Figs. 1, 2 and 3 is desirably manufactured in accordance with the method and apparatus illustrated in Figs. 7 to 14, inclusive. The apparatus of Figs. 12, 13 and 14 may also serve for applying primer to, and connecting the bases to the bulbs of, the lamps of Figs. 15, 16, 17 and 20. The base 24 is desirably made of a plastic material such as designated by the trademark ,Vinnapasf This is a so-called sealing plastic manufactured by Dr. Alexander Wacker Gesellschaft fr Elektrochemisch Industrie, G. m. b. H., 22 Prinzregentenstrasse, Munich, Germany. However, other solid plastic materials which have melting points lower than that of the bulb 22, to which connected, may be employed.

The lead-in conductor 25 is desirably formed from #24 soft iron wire 31 and coated with a vinyl plastic. It may be of a type used in the electrical and artificial flower industries. It is furnished on spools and supplied by either Alpha Wire Corp., 430 Broadway, New York, N. Y., or Birnbach Radio Co., 145 Hudson Street, New York, N. Y. The plastic is stripped from the wire at one end and slid beyond the wire, or the wire cut off short of the plastic, at the other end to form the lead 25, as shown in Fig. 10. Apparatus for performing this operation is shown fragmentarily in Figs. 7, 8 and 9.

The wire 31, as it comes from the spool, is represented in Figs. 7 and 8. The desired length, after passing between straightening rollers 32, is drawn by jaws 34 and 35 which, at each full reciprocation after gripping, pull wire of a length designated by the arrow 36. While so gripped, a pair of jaws 37 and 38 first cut through the plastic coating sufiiciently, as indicated in Fig. 8, and then push it back, or to the right as viewed in Fig. 8, finally cutting off the bared wire at the point designated 39. When released, the plastic comes back to a position beyond the end of said wire, represented by the distances between the arrows 41 and 42 in Fig. l0.

At about the same time, the other end portion of the wire is engaged by cutting jaws 43 and 44, notched as indicated at 45 in Fig. 9, so that the bared wire portion 46 is not cut, but only some of the insulation 47. In this way, a length of insulation is stripped from the opposite end portion of the wire, leaving the bared wire 46, as viewed in Figs. 8 and 9.

The next operation is to introduce the bare wire portion 46 into the plastic base 24. This may be accomplished, as viewed in Fig. 10, by heating said bare wire, as by means of an electrical heater device 48 contacting the same, so as to enable it to melt plastic and pass through the center of the base 24, before or after cutting CII from a rod of plastic, as while said base is resting on a support 49, apertured as indicated at 51 to allow the lower end portion of said wire to pass therethrough.

An alternative method of introducing the wire through the plastic base 24 is shown in Fig. 11, in which relative rotation between the parts, represented by the arrow 52, makes it possible to pass the wire portion 46 into the plastic base 24 by the generated frictional heat, the melted plastic immediately tightly sealing about the wire 46 after motion is stopped.

After forming the base and lead assembly, as illustrated in Fig. 11, the same is reversed and while held in jaws 53 and 54, a reciprocable cup 55 is raised from a bath 56 of priming material supported as by means of the rod 57. This apparatus for applying priming material, to the insulation-carrying end of the lead 25, may be such as disclosed and claimed in the application of Thomas Hamilton, entitled Coating Mechanism, Serial No. 351,- 385, filed April 27, 1953, now Patent No. 2,703,552, and owned by the assignee of the present application. By the use of this mechanism the primer material is kept in a properly stirred condition resulting in uniformity in the amount applied at each dip because the consistency of the primer is maintained. However, I do not wish to limit myself to the application of priming material by such a machine, as such application may be effected by conventional means.

After application of the primer 5S to the lead 25 over the insulation 47, the former is allowed to dry and the mount so constructed then reversed in position. The base 24 is inserted in a cup 59 mounted on the upper end of a reciprocable rod 61 and carrying a light spring 62 in its interior. The cup is disposed in an exhaust-andgas-filling chamber 63, which for the purpose is connected to an exhaust and gas filling system, as by means of a pipe 64. Leakage between the rod 61 and the lower wall of the chamber is prevented by means of a sealing bellows arrangement 65, desirably of the so-called sylphon type.

ln the chamber 63 is mounted a coil of oxygen-resisting Nichrome or other heating wire 66, surrounding the cup 59. Leads 67 and 68 connect the wire 66 to a source of power for energizing the same to soften the base 24, when resiliently supported in the cup 59, as viewed in Fig. 13. The chamber 63 opens upwardly and is partially closed by the rubber or other resilient cover 69, apertured as indicated at 71 to receive the neck 23 of the bulb 22, while nesting with the main or bulbular portion thereof to provide an air-tight engagement.

The manner of operating the apparatus for uniting the base to a bulb, after exhausting and gas filling, is as follows: A mount comprising a base 24, lead 25, and primer 26 is placed, as viewed in Fig. 13, with the base resting on the spring 62 and disposed in the cup 59. A bulb 22 carrying combustible material of conventional character 29, for example, is then placed over the primer 26 to close the aperture 71 as viewed in Fig. 13. The air in the chamber 63 and connected bulb is then exhausted, while the coil 66 is energized to soften the base 24.

After exhausting t-o the desired extent, oxygen or other combustion-supporting gas is introduced to the chamber 63, from whence it passes to the bulb 22, said bulb during the operation being held in place by a suitable chuck 72.. When filling gas at the desired pressure has been introduced and the base 24 sufficiently softened, the rod 61 is raised to push the base 24 into sealing engagement with the lower edge or neck 23 of said bulb. This movement is completed by a follow-through of the cup beyond the upper edge -of the base, against the pressure of the spring 62, to the position illustrated in Fig. 14, so as to push thc outer and upper edge portion of the base about the neck portion of the bulb, to effect a proper sealing engagement. The base is then allowed to cool and the lamp removed.

Referring now to the embodiment of my invention illustrated in Figs. 15 and 16,'there is shown a photoflash lamp 21a comprising an envelope or bulb 22a of translucent material such as glass, the edge of the neck 23a of which is embedded ina block of plastic 24a which forms a base. A lead` 251L projects through said base 24a, so that the outer end thereof forms a contact or means for introducing igniting, power to the lamp, while the inner end thereof carries priming material 26ab and one end of a priming filament 60.

In the present embodiment, there is also used a second lead 73, which carries priming material 7.0, supports the other end of the filament 60, and extends parallel to the lead 25a toward the outer end portion thereof. It however, near the outer end turns at an approximate right angle and extends out the side of the base, forming a contact lug or prong 74. The prong 74 is secured to a contact plate 75', as by bending the lower edge portion thereof into a-partially cylindrical collar 76 and brazing or otherwise securing the prong portion of the lead therein. In this way, a photoash lamp, is produced approximating one with a conventional bayonet-type base, except that onlyV one lug 74 is here provided.

Referring now to the embodiment of my invention illustrated in Fig. 17, there is shown a photoilash lamp 2lb comprising an envelope or bulb 22", of translucent material such as glass, the edge of the neck 23b of which is embedded in a block of plastic 24h, which forms a base. Leads 25h and 73b project from said base and carry thereon priming material and therebetween a priming lila ment 60h, as in the preceding embodiment.

In the present embodiment, however, the lead 73h, insteadL of turning at an approximate right angle and extending out of the side of the base, forming a Icontact lug or prong 74lo secured to a mere contact plate, as in the preceding embodiment, said prong is secured in a similar manner to a hollow cylindrical contact band 75h, which encircles the periphery of the base, being embedded therein so that its outer surface is flush with the outer surface ofplastic base. Except for this change, the embodiment of Fig. 17 corresponds with that of Figs. 15 and 16.

A base for alamp as illustrated in Figs. 15 and 16 or as illustrated in Fig. 17, may be produced with apparatus illustrated in Figs. 18 and 19. This apparatus comprises a lower mold 77 having a pipe 78 leading from its mold cavity 79 to a source of compressed air. The mold cavity 79 is for receiving4 the material to form the plastic base 24?'. It has a restricted extension 81 therebeneath through which compressed air may be introduced to -control the flow of molten plastic into said extension, push said plastic into the upper mold, and eject the base after forming. Two lower pockets 82 and 83 are provided for receiving the ends of the leads 25"L and 73, or 25h and 73h, respectively, as the case may be. A side pocket 84 is also provided for receiving the prong or side contact portion 74 of the lead 73. -An upper mold S is provided with an axial aperture 86 for receiving the end of the lead 25a which is uppermost in the positions of Figs. 18 and 19. This upper mold has side flanges 87, for guidingly nesting over the top of the lower mold 77, and a central portion 88 formed to give the desired shape to the base where the center contact emerges.

Bases are formed in the molds heretofore described by pouring molten plastic material 89, as from a container 91, into the lower mold 77, after rst placing therein the leads 25a, 73 and the connected contact plate 75, or the leads 23h, 73b and the connected contact band 75h, as the case may be. The ends ofthe leads lie in the lower pockets 82 and 83, respectively, with the side prongportion 74 or 74", in the side pocket 84 and the plate 75 or band 75b contacting the side wall of the mold cavity 79. After pouring a suiiicient amount of plastic material 89 into the mold to produce a base, said material being prevented from flowing further than illustrated in Fig. 19 by pres'- sure of airintroduced through the pipe 78, the upper mold member is brought down to form the surface of the base, which when made into a lamp becomes the lower. surface as viewed in Figs. 15 and 16. The air pressure is increased sufficiently so that the plastic material entirely fills the cavity between the upper and lower molds. After the plastic material has lcooled sutiiciently, the upper moldA 85 is withdrawn and the formed base` ejected by increasing the pressure of the air introduced through the pipe 7S..

The formed base 24a may be united with a glass bulbv 22a in a manner similar tothe uniting of aV base 24 with a glass bulb 22, as described in connection with the apparatus illustrated in Figs. 13 and. 14, except that instead of dipping the bulb-receiving ends of the leads 25a and '73 in primer, using apparatus illustrated Vin Fig. 12, for example, a primer filament 60 is first attached to said leads in a conventional manner and then the primer material 26a' and 70 applied to the filament-connected' ends, in accordance with normal procedure.

Figure 20 is a view similar to Fig. 15, but illustrating another embodiment of my invention comprisinga photoflash lamp 21c provided with an envelope or bul-b 22c of translucent material such as glass, the edge of the neck 23c of which is embedded in a block of plastic 24C which forms a base. In addition to the-leads, 25c and 73 corresponding respectively with the leads 25a and 73 of a preceding embodiment, and the contact plate 75c and prong 74 respectively corresponding with the parts 75 and 74 of said preceding embodiment, in the present embodiment an auxiliary lead 92, parallels part way the lead 73c and extends into the plastic, turning at an. angle to project out of the side thereof, forming a contact prong 93, desirably diametrically oppositethe prong 74C. There is also provided a corresponding contact plate 94, connected to said prong like the plate 75C is connected to the prong 74C, both of said plates and all of the leads being embedded in the plastic base like the leads and plate of the embodiment of Figs. 15 and 16. It will also be understood that l may substitute a band, like that designated 75o in Fig. 17, for the two plates 75c and 94, the construction being otherwise identical.

The base of the embodiment of Fig. 20 may be formed in a mold (not shown) but corresponding with the mold 77, except that an additional bottom pocket and an additional side pocket are provided for the reception of the lower end and side prong portion 93 of the lead 92. After molding, the lead 92, instead of being left straight like the lead 73, is bent at an angle and around the lead 25c as indicated at 95, and welded or otherwise secured to the leads 73C, as indicated at 96. In this way, I have provided a photoflash lamp which is interchangeable with the conventional bayonet-type base lamp, by having two side prongs instead of only one.

In Fig. 4, I have shown a wiring diagram of apparatus illustrated in Fig. 5 and Fig. 6, which may be employed for operating or igniting lamps embodying my invention. In this diagram, the reference character 96 represents the casing of a flash pack or igniting apparatus.. Enclosed therein is a battery 97, desirably of the 221/2 volt hearingaid dry cell type. Connected to said battery is a resistor 98, of preferably about 10,000 ohms, and a condenser 99, of preferably about 5() microfarads capacity, said condenser being across the battery terminals with the resistor in series.

The condenser terminals are in turn connected through a switch 101, which may connect through contact prongs or sockets 107 and 108, across the terminals of the primary winding 102 of a step-up transformer 103. The secondary winding 104 has one terminal connected to a terminal of the primary winding 102, and the other terminal connected to the lead 25 of a photoflash lamp 2l. Withl this arrangement, the condenser is slowly charged through the resistor 99 and always in condition for delivering a desired surge of electrical energy through the primary winding 102 of the transformer upon closingV the switch 101.

The ratio between the turns of the primary and secondary windings is desirably such that a potential of at least 10,000 volts is delivered to the lead 25 on closing the switch 101, to thereby produce a discharge between the inner end of said lead and the primer material 26, across the spark gap left between the end of the lead 25 and the end of the insulation 27, thereby igniting said primer and through it the surrounding combustible material 29.

The apparatus described may be also employed for operating or igniting lamps 21a, 2lb and 21C, represented in dotted lines, the only difference being that the transformer 103 is not employed, the leads to the lamp being connected across the terminals of the condenser 99, through the switch 101, as by conductors 10S and 19d, so that upon the condenser discharging through the filament 60, 60h or 60, said filament is incandesced and ignites the primer and through it the combustible material 29?', 29h or 29? surrounding it, as will be understood.

Fig. is an embodiment of apparatus employing the circuit of Fig. 4. in this figure, the part 97a represents the battery, the condenser being therebeneath and enclosed in the shell or casing 96a. The part la represents the transformer, the primary winding of which is connected across the terminals of the condenser (not shown) through an external switch (not shown), the leads from which are respectively connected to the contact prongs '7a and 103g.

A photoash lamp 21 is received in a socket 109, desirably provided with a coiled annular spring 111 or other means which frictionally grips the base 24 and holds it in place, so that a discharge to the lead 25 thereof may be effected through contact pin 112 from terminal 113 of the secondary winding of the transformer 1038'. The other terminal 114 of the secondary winding is connected to the Contact prong 107e. A reflector 115 is connected to the device, as by means of set screws 116. lt will be understood that the apparatus just described is intended for igniting only improved photoilash lamps of the type illustrated in Figs. 1, 2 and 3, as those of the type of Figs. 15, 17 and 20 may be ignited in accordance with conventional apparatus, or that now on the market, as will be understood.

The apparatus of Fig. 6 is like that of Fig. 5, except that it shows conventional apparatus suitable for igniting photoash lamps of the type of Figs. l5, 17 and 2O provided with an adapter 118 including a transformer 103k, making it possible to also ignite lamps of the type designated 21, of Figs. 1, 2 and 3. Thus, the apparatus comprises a battery 97h, a condenser 99h, and a resistor 93b connecting the same. One terminal of the condenser is connected to a contact socket 10312 the other terminal being connected to one side of the primary winding of the transformer 103b through the casing 96h, screw 110, shell 120 of the adapter base, and contact 123 mounted thereon.

The other terminal of the primary winding is connected to one terminal of the secondary winding and also through contact 122, which is connected to the center contact 117 of the adaptor base, to the contact socket 107i. The other terminal of said secondary winding is connected to a center contact, 112ID of the device, which in this instance is also the iron core of the transformer 1031. The resistor 98h is connected between the remaining terminals of the battery and condenser, that is, between lower terminal of the battery 97b and the lower terminal of the condenser 99h, as viewed in Fig. 6. A yoke device 126 and springs 127 (only one of which is seen in Fig. 6) serve to hold the battery in place on top of the condenser, which rests on spring 128. In the present instance, the transformer 103b fits in the customary reiector 119, the reflector 115l being connected to the socket portion 109b of the adapter 118 as by means of rivets 121. The socket 109'@ may be equipped with a friction spring 111b like the socket 109, and it is so threaded with respect to the shell 120 that clockwise rota- -8 tion of the reflector 115b closes the space between the latter and the reflector 119 of a standard gun assembly.

Although preferred embodiments of my invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the invention.

I claim:

1. A photoash lamp comprising, a sealed and radiation-transmitting bulb with a neck, a base secured to said neck, a contact electrode provided on the external surface of said base, a filling of shredded actinic foil and an oxidizing atmosphere contained within said bulb, an electrically-conducting lead projecting within said bulb, said lead electrically connected to said contact electrode, an insulating coating carried on said lead, an electricalbreakdown path through said insulating coating, a primer material carried directly on said insulating coating and over said electrical-breakdown path, a portion of said foil contiguous with said primer material, an electricdischarge path formed by said electrical-breakdown path and said primer material, and the breakdown voltage of said electric-discharge path being such that any electric discharge from said conducting lead to said shredded foil must contact said primer.

2. A photoflash lamp comprising, a sealed and radiation-transmitting bulb with a neck, a base secured to said neck, a contact electrode provided on the external surface of said base, a filling of shredded aluminum foil and an oxygen atmosphere contained within said bulb, an electrically-conducting lead projecting within said bulb, said lead electrically connected to said contact electrode, an insulating coating carried on said lead, an electrical breakdown path through said insulating coating, a primer material carried directly on said insulating coating and over said electrical-breakdown path, a portion of said foil contiguous with said primer material, an electric-discharge path formed by said electrical-breakdown path and said primer material, and the breakdown voltage of said electric-discharge path being such that any electric discharge from said conducting lead to said shredded foil must contact said primer.

3. A phototlash lamp comprising, a sealed and radiation-transmitting bulb, a contact electrode forming a part of said lamp and positioned external to said sealed bulb, a filling of shredded actinic foil and an oxidizing atmosphere contained within said bulb, an electrically-conducting lead projecting within said bulb, said lead electrically connected to said contact electrode, an insulating coating carried on said lead, an electrical-breakdown path through said insulating coating, a primer material carried directly on said insulating coating and over said electrical-breakdown path, a portion of said foil contiguous with said primer material, an electric-discharge path formed by said electrical-breakdown path and said primer material, and the breakdown voltage of said electric-discharge path being such that any electric discharge from said conducting lead to said shredded foil must contact said primer.

4. A photoflash lamp comprising, a sealed and radiation-transmitting bulb, a contact electrode forming a part of said lamp and positioned external to said sealed bulb, a filling of shredded aluminum foil and an oxygen atmosphere contained within said bulb, an electrically-conducting lead projecting within said bulb, said lead electrically connected to said contact electrode, an insulating coating carried on said lead, an electrical-breakdown path through said insulating coating, a primer material carried directly on said insulating coating and over said electrical-breakdown path, a portion of said foil contiguous with said primer material, an electric-discharge path formed by said electrical-breakdown path and said primer material, and the breakdown voltagerof said electric-discharge path being such that any electric discharge from said conducting lead to said shredded foil must contact said primer.

(References on following page) References Cited in the le of this patent UNITED STATES PATENTS Williams Feb. 23, 1937 Williams Feb. 23, 1937 Kower Apr. 26, 1938 l0 Ledig Nov. 25, 1941 Margitta Feb. 24, 1942 Fulton July 22, 1947 Malone Oct. 21, 1952 Fairbank July 28, 1953 

